Modern multi-step variable-speed transmissions such as automated variable-speed transmissions, planetary automatic transmissions and dual-clutch transmissions can be operated both in a manual mode and in an automatic mode. In the manual mode shifts can be initiated directly by the driver, for example when the driver uses his hand to move a shift lever provided for the purpose in an upshift direction or in a downshift direction. In contrast, in the automatic mode shifts are initiated automatically, in that current vehicle, road and driver-specific operating parameters, such as the current driving speed, the current driving acceleration, the current engine speed, the current engine torque, the current vehicle mass, the current road inclination (uphill, level, downhill), the current driving resistance and the current driver's wish (a power demand by the driver or by a cruise control), are determined and shifts are initiated with reference to shift performance graphs or shift characteristic curves. The current operating parameters can either be measured directly or calculated from measured values. For example, the current driver's wish can be deduced by means of an associated characteristic curve, from the position of the accelerator pedal, which can be measured by a potentiometer. In improved processes, the calculable rate of change of the accelerator pedal's position can additionally be used for this.
It is true that in most operating situations, shift control of automated variable-speed transmissions that is based on current operating parameters gives good results, so far as high driving dynamics, low fuel consumption and a high level of shifting and driving comfort are concerned. However, particularly in the transition zone between different road inclinations and driving resistances, inappropriate shifts often occur because conventional shift control methods do not take into account the topography of the road section ahead of the motor vehicle. For example, before reaching the brow of a hill a downshift may be initiated although the vehicle could drive over the brow of a hill with little loss of speed even in the currently engaged gear, so that the downshift and a subsequent upshift could have been avoided.
Likewise, when an uphill stretch is known to be approaching it is advantageous to shift down to a lower gear even before beginning to drive up the slope, since the vehicle can then drive up at a higher speed and a further downshift can perhaps be avoided. Moreover, when moving from a downhill stretch onto level ground it is expedient, even before reaching the level stretch, to upshift to a higher gear since by doing this, using the kinetic energy of the motor vehicle it can be driven onto the level stretch at a higher speed so that transition to traction operation takes place later.
Thus, to improve the shifting behavior of automated multi-step variable-speed transmissions some methods and devices have already been proposed, which provide for the detection of topographical data regarding a road section ahead of the motor vehicle, in particular its height profile, and for taking this into account for controlling shifts in an automated transmission.
For example, DE 101 29 149 A1 proposes a method for optimizing the force transmission from an engine to the drive wheels of a vehicle, in which method road and map data from a navigation system are also used when specifying nominal values for controlling the engine and/or the transmission. This known method provides that from the road and map data of the navigation system information is determined concerning the road section ahead, such as road inclination, road curvature (curve radius) and other attributes of the road and its surroundings, and from that information control commands for controlling the transmission and/or the engine are derived.
DE 10 2006 001 818 A1 describes a method and device for assisting the driver during the driving operation of a motor vehicle, in which the topographical data relating to a road section of the drive route ahead of the motor vehicle are called up from a memory and evaluated by the transmission control system, with computer support, when adjusting driving operation components, in particular when setting a gear in the transmission. The topographical data can be stored in the form of a height profile or an inclination profile of the drive route concerned.
Finally, from DE 10 2005 050 753 A1 a method and device for controlling and/or regulating an automatic system of a motor vehicle is known, in which, to determine the nature of a road stretch ahead of the motor vehicle, data are collected and combined to form a driving resistance profile of the motor vehicle. The driving resistance profile determined is intended, among other things, to be used in an automatic transmission for producing the transmission gear ratio most suitable for the stretch ahead of the motor vehicle.
It is true that the known methods and devices provide useful approaches for improving the shifting behavior of automated multi-step variable-speed transmissions. However, the documents cited do not provide concrete indications about how, from the topographical data relating to the road section ahead of the motor vehicle, such as its height profile, its inclination profile or the vehicle's driving resistance profile, specific control commands should be derived and implemented in the transmission control system.